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Abstract:

An apparatus and method for controlling a whitening function of a
whitening Maximum Ratio Combining (MRC) in a receive end of a multiple
antenna system are provided. The method includes identifying if there is
interference from at least one neighbor cell, if there is interference,
generating a weight of the whitening MRC using a pre-whitening inverse
matrix, and, if there is no interference, generating a weight of the
whitening MRC using a unit matrix, thus being capable of improving a
reception performance of the receive end.

Claims:

1. A method for controlling a whitening function of a whitening Maximum
Ratio Combining (MRC) in a receive end of a multiple antenna system, the
method comprising the steps of: identifying if there is interference from
at least one neighbor cell; if there is interference, generating a weight
of the whitening MRC using a pre-whitening inverse matrix; and if there
is no interference, generating a weight of the whitening MRC using a unit
matrix.

2. The method of claim 1, wherein identifying if there is interference
comprises: measuring an interference power using a receive signal;
comparing the interference power with a threshold interference power; and
identifying if there is interference from the neighbor cell based on the
comparison.

3. The method of claim 2, wherein measuring the interference power
comprises: measuring power of a combination of noise and interference
using a pilot included in the receive signal; measuring a power of at
least one unused tone; removing the power of the at least one unused tone
from the power of the combination of noise and interference; and
identifying the interference power.

4. The method of claim 1, wherein identifying if there is interference
comprises: calculating a Carrier to Interference plus Noise Ratio (CINR)
using a receive signal; comparing the CINR with a threshold CINR; and
identifying if there is interference from the neighbor cell based on the
comparison.

5. The method of claim 1, wherein the pre-whitening inverse matrix is
generated through Cholesky Factorization of a covariance matrix of noise
plus interference.

6. An apparatus for controlling a whitening function of a whitening
Maximum Ratio Combining (MRC) in a receive end of a multiple antenna
system, the apparatus comprising: at least one antenna; an interference
identifier for identifying if there is interference from at least one
neighbor cell, using a signal received through the at least one antenna;
a filter controller for, if there is interference, providing a
pre-whitening inverse matrix to a pre-whitening filter and, if there is
no interference, providing a unit matrix to the pre-whitening filter; and
the pre-whitening filter for generating a weight of the whitening MRC
using the pre-whitening inverse matrix or unit matrix provided from the
filter controller.

7. The apparatus of claim 6, wherein the interference identifier compares
an interference power measured using the receive signal with a threshold
interference power, and identifies if there is interference from the
neighbor cell based on the comparison.

8. The apparatus of claim 7, wherein the interference identifier removes
power of at least one unused tone from a power of a combination of noise
and interference measured using a pilot included in the receive signal,
and identifies an interference power.

9. The apparatus of claim 6, wherein the interference identifier compares
a Carrier to Interference plus Noise Ratio (CINR) calculated using the
receive signal with a threshold CINR, and identifies if there is
interference from the neighbor cell based on the comparison.

10. The apparatus of claim 6, wherein, if there is interference, the
filter controller provides a pre-whitening inverse matrix, which is
generated through Cholesky Factorization of a covariance matrix of noise
plus interference, to the pre-whitening filter.

Description:

PRIORITY

[0001] This application is a Divisional Application of U.S. patent
application Ser. No. 12/704,281 filed in the U.S. Patent and Trademark
Office on Feb. 11, 2010 and claims priority under 35 U.S.C. §119(a)
to a Korean Patent Application filed in the Korean Intellectual Property
Office on Feb. 10, 2009 and assigned Serial No. 10-2009-0010464, the
contents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a pre-whitening filter of a
receive end in a multiple antenna system. More particularly, the present
invention relates to an apparatus and method for selectively using a
Minimum Mean Square Error (MMSE) scheme or a Maximum Ratio Combining
(MRC) scheme depending on the existence or absence of inter-cell
interference in a receive end of a multiple antenna system.

[0004] 2. Description of the Related Art

[0005] With a rapid growth of the wireless mobile communication market,
there is an increase in the demand for diversity of multimedia services
in the wireless environment. Accordingly, as a large capacity of
transmission data and a high speed of data transmission are implemented
to provide multimedia services, extensive research of multiple antenna
systems capable of efficiently using limited frequency resources is being
conducted.

[0006] The multiple antenna system can increase transmission reliability
and data rate compared to a single antenna system without additional
frequency or transmission power allocation through data transmission
using an independent channel.

[0007] The typical receiving method used in the multiple antenna system
can be an MMSE scheme and an MRC scheme. In the environment in which
there is inter-cell interference, an MMSE receive end has more excellent
reception performance than an MRC receive end. However, when there is no
inter-cell interference, the MMSE receive end exhibits a lesser reception
performance than the MRC receive end. For example, when there is no
inter-cell interference, the MMSE receive end has poor reception
performance because off-diagonal elements do not converge to `0` at the
time when the Rnn-1 calculation necessary for MMSE weight
calculation is performed.

[0008] Thus, a receive end of a multiple antenna system needs a method for
selectively using an MMSE scheme or an MRC scheme depending on the
existence or absence of inter-cell interference to improve reception
performance.

SUMMARY OF THE INVENTION

[0009] The present invention substantially solves at least the above
problems and/or disadvantages and provides at least the advantages below.
Accordingly, one aspect of the present invention is to provide an
apparatus and method for selectively using a Minimum Mean Square Error
(MMSE) scheme or a Maximum Ratio Combining (MRC) scheme depending on the
existence or absence of interference in a receive end of a multiple
antenna system.

[0010] Another aspect of the present invention is to provide an apparatus
and method for controlling a whitening function of a whitening MRC
depending on the existence or absence of interference in a receive end of
a multiple antenna system.

[0011] A further aspect of the present invention is to provide an
apparatus and method for controlling a whitening function of a whitening
MRC depending on a Carrier to Interference plus Noise Ratio (CINR) in a
receive end of a multiple antenna system.

[0012] The above aspects are achieved by providing an apparatus and method
for adaptive whitening in a multiple antenna system.

[0013] According to one aspect of the present invention, a method for
controlling a whitening function of a whitening Maximum Ratio Combining
(MRC) in a receive end of a multiple antenna system is provided. The
method includes identifying if there is an influence of interference from
at least one neighbor cell, if there is the influence of interference,
generating a weight of the whitening MRC using a pre-whitening inverse
matrix, and, if there is no influence of interference, generating a
weight of the whitening MRC using a unit matrix.

[0014] According to another aspect of the present invention, a method for
controlling a whitening function of a whitening MRC in a receive end of a
multiple antenna system is provided. The method includes identifying if
there is an influence of interference from at least one neighbor cell,
setting an update variable for a covariance matrix of noise plus
interference in consideration the influence of interference, calculating
a covariance matrix of noise plus interference, updating the covariance
matrix of noise plus interference using the update variable, calculating
a pre-whitening inverse matrix using the updated covariance matrix of
noise plus interference, and generating a weight of the whitening MRC
using the pre-whitening inverse matrix.

[0015] According to a further aspect of the present invention, an
apparatus for controlling a whitening function of a whitening MRC in a
receive end of a multiple antenna system is provided. The apparatus
includes at least one antenna, an interference identifier, a filter
controller, and a pre-whitening filter. The interference identifier
identifies if there is an influence of interference from at least one
neighbor cell, using a signal received through the at least one antenna.
If there is an influence of interference, the filter controller provides
a pre-whitening inverse matrix to the pre-whitening filter and, if there
is no influence of interference, the filter controller provides a unit
matrix to the pre-whitening filter. The pre-whitening filter generates a
weight of the whitening MRC using the pre-whitening inverse matrix or
unit matrix provided from the filter controller.

[0016] According to a yet another aspect of the present invention, an
apparatus for controlling a whitening function of a whitening MRC in a
receive end of a multiple antenna system is provided. The apparatus
includes at least one antenna, an interference identifier, a filter
controller, and a pre-whitening filter. The interference identifier
identifies if there is an influence of interference from at least one
neighbor cell using a signal received through the at least one antenna.
The filter controller updates a covariance matrix of noise plus
interference using an update variable for a covariance matrix of noise
plus interference that is set considering an influence of interference,
and transmits a pre-whitening inverse matrix, which is calculated using
the updated covariance matrix, to the pre-whitening filter. The
pre-whitening filter generates a weight of the whitening MRC using the
pre-whitening inverse matrix provided from the filter controller.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present
invention will become more apparent from the following detailed
description when taken in conjunction with the accompanying drawings in
which:

[0019]FIG. 2 is a block diagram illustrating a receive end in a multiple
antenna system according to the present invention;

[0020]FIG. 3 is a flow diagram illustrating controlling a whitening
function depending on an interference amount in a receive end according
to an embodiment of the present invention;

[0021] FIG. 4 is a flow diagram illustrating controlling a whitening
function depending on an interference amount in a receive end according
to another embodiment of the present invention;

[0022] FIG. 5 is a flow diagram illustrating controlling a whitening
function depending on a Carrier to Interference plus Noise Ratio (CINR)
in a receive end according to an embodiment of the present invention; and

[0023]FIG. 6 is a flow diagram illustrating controlling a whitening
function depending on a CINR in a receive end according to another
embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

[0024] The following description with reference to the accompanying
drawings is provided to assist in a comprehensive understanding of
exemplary embodiments of the invention as defined by the claims and their
equivalents. It includes various specific details to assist in that
understanding but these are to be regarded as merely exemplary.
Accordingly, those of ordinary skill in the art will recognize that
various changes and modifications of the embodiments described herein can
be made without departing from the scope and spirit of the invention.
Also, descriptions of well-known functions and constructions are omitted
for clarity and conciseness.

[0025] The terms and words used in the following description and claims
are not limited to their dictionary meanings, but are merely used to
enable a clear and consistent understanding of the invention.
Accordingly, it should be apparent to those skilled in the art that the
following description of embodiments of the present invention are
provided for illustration purpose only and not for the purpose of
limiting the invention as defined by the appended claims and their
equivalents.

[0026] A technology for selectively using a Minimum Mean Square Error
(MMSE) scheme or a Maximum Ratio Combining (MRC) scheme depending on the
existence or absence of inter-cell interference in a receive end of a
multiple antenna system is described below.

[0027] In the following description, it is assumed that the receive end
includes NR antennas. Here, the `NR` represents an integer of
`1` or more.

[0028] Also, in the following description, it is assumed that the multiple
antenna system uses an Orthogonal Frequency Division Multiplexing (OFDM)
scheme. However, the present invention is applicable even when the
multiple antenna system uses other communication schemes.

[0029] When there is inter-cell interference, the receive end receives a
signal that can be represented as in Equation (1). Here, Equation (1)
represents a receive signal converted into a frequency domain signal
through Fast Fourier Transform (FFT).

Y=HX+HII+N (1)

[0030] In Equation (1), `Y` represents a signal received at a receive end,
`H` represents a channel between a transmit end and the receive end, `X`
represents a signal transmitted at the transmit end, `H.sub.I` represents
an interference channel between a different transmit end having the
influence of interference and the receive end, T represents a neighbor
cell interference signal, and `N` represents a thermal noise.

[0031] When the receive end uses an MMSE scheme, the receive end generates
an MMSE weight based on Equation (2).

W=E[xyH]E[yyH]-1=HHR-1yy=HHR-1.s-
ub.nn (2)

[0032] In Equation (2), `W` represents an MMSE weight, `y` represents a
receive signal, `H` represents a channel between a transmit end and a
receive end, and `Rnn` represents a covariance matrix of noise plus
interference. Here, `HHR1yy=HHR1nn` can be
proved by applying a matrix inversion theorem.

[0033] The covariance matrix (Rnn) of Equation (2) can be given using
Cholesky Factorization as in Equation (3).

[0035] By applying Equation (3) to Equation (2), the MMSE weight can be
expressed in Equation (4).

W=HHR-1nnH=HH(LLH)-1=(L-1H)H(L)-1 (4)

[0036] In Equation (4), `W` represents an MMSE weight, `H` represents a
channel between a transmit end and a receive end, `Rnn` represents a
covariance matrix of noise plus interference, and `L` represents a
pre-whitening inverse matrix.

[0037] When the receive end uses an MRC scheme, the receive end generates
an MRC weight given in Equation (5).

WMRC=HH (5)

[0038] In Equation (5), WMRC` represents an MRC weight, and `H`
represents a channel between a transmit end and a receive end.

[0039] In a comparison between Equations (4) and (5), the MMSE weight and
MRC weight have a difference of application/non-application of a
pre-whitening inverse matrix (L). Accordingly, as illustrated in FIG. 1
the receive end can selectively use an MMSE scheme or an MRC scheme by
controlling the pre-whitening inverse matrix (L) of a whitening MRC
depending on the existence or absence of interference. Here, the
whitening MRC represents a reception scheme designed to exhibit the
reception performance of the MMSE scheme using an MRC.

[0040] FIG. 1 is a block diagram illustrating whitening MRC according to
the present invention.

[0041] As illustrated in FIG. 1, the whitening MRC multiplies a weight by
a pre whitening inverse matrix (L) to receive the same signal as that of
an MMSE scheme. At this time, a receive end selectively provides the
pre-whitening inverse matrix (L) depending on the existence or absence of
interference and turns ON/OFF a whitening function of the whitening MRC.
For example, when there is inter-cell interference, the receive end
provides the pre-whitening inverse matrix (L). Accordingly, the receive
end can generate an MMSE weight given in Equation (4) and receive the
same signal as that of the MMSE scheme. As another example, when there is
no inter-cell interference, the receive end provides a unit matrix (kI),
not the pre-whitening inverse matrix (L). Accordingly, the receive end
can generate an MRC weight given in Equation (5) and receive the same
signal as that of an MRC scheme.

[0042] The following description is that of a receive end for selectively
providing a pre-whitening inverse matrix depending on the existence or
absence of interference.

[0043]FIG. 2 is a block diagram illustrating a receive end in a multiple
antenna system according to the present invention.

[0044] As illustrated in FIG. 2, the receive end includes a plurality of
Radio Frequency (RF) receivers 201-1 to 201-NR, a plurality of
Analog to Digital Converters (ADCs) 203-1 to 203-NR, a plurality of
OFDM demodulators 205-1 to 205-NR, a plurality of interference
measurement units 207-1 to 207-NR, a plurality of filter controllers
209-1 to 209-NR, a pre-whitening filter 211, and a Multiple Input
Multiple Output (MIMO) detector 213.

[0045] The RF receivers 201-1 to 201-NR convert signals received
through antennas (N1 to NR) into baseband signals.

[0047] The OFDM demodulators 205-1 to 205-NR convert time domain
signals provided from the respective ADCs 203-1 to 203-NR into
frequency domain signals through a Fast Fourier Transform (FFT)
operation.

[0048] The interference measurement units 207-1 to 207-NR measure
interference power in signals provided from the respective OFDM
demodulators 205-1 to 205-NR. For example, the interference
measurement units 207-1 to 207-NR measure power of a combination of
noise and interference using pilot signals. The interference measurement
units 207-1 to 207-NR measure power of unused tones. If the
interference measurement units 207-1 to 207-NR recognize the sum of
the power of the unused tones as thermal noise, the interference
measurement units 207-1 to 207-NR remove the thermal noise from the
power of combination of noise and interference and measure interference
power.

[0049] As another example, when measuring covariance matrices (Rnn)
of noise plus interference in a burst, the interference measurement units
207-1 to 207-NR can also measure interference power in the burst.

[0050] As a further example, in the case of an Adaptive Modulation and
Coding (AMC) sub-channel structure, the interference measurement units
207-1 to 207-NR can also measure interference power in a band.

[0051] The filter controllers 209-1 to 209-NR determine if there is
interference depending on interference power provided from the respective
interference measurement units 207-1 to 207-NR, and select
pre-whitening inverse matrices (L). For example, when there is
interference, the filter controllers 209-1 to 209-NR select and
provide pre-whitening inverse matrices (L) to the pre-whitening filter
211. As another example, when there is no interference, the filter
controllers 209-1 to 209-NR select and provide unit matrices (kI) to
the pre-whitening filter 211.

[0052] The pre-whitening filter 211 filters out interference from receive
signals provided from the OFDM demodulators 205-1 to 205-NR. The
pre-whitening filter 211 is included in a whitening MRC. Accordingly,
when receiving pre-whitening inverse matrices (L) from the filter
controllers 209-1 to 209-NR, the pre-whitening filter 211 generates
an MMSE weight given in Equation (4) and receives a signal in an MMSE
scheme. On the other hand, when receiving unit matrices (kI) from the
filter controllers 209-1 to 209-NR, the pre-whitening filter 211
generates an MRC weight given in Equation (5) and receives a signal in an
MRC scheme.

[0053] The MIMO detector 213 determines a transmit signal using a receive
signal from which interference is filtered out by the pre-whitening
filter 211 and channel information.

[0054] The following description is a method for controlling a whitening
function depending on the existence or absence of interference that is
identified using interference power.

[0055]FIG. 3 is a flow diagram illustrating controlling a whitening
function depending on an interference amount in a receive end according
to an embodiment of the present invention.

[0056] Referring to FIG. 3, in step 301, the receive end identifies if a
signal is received from a transmit end.

[0057] If the signal is received from the transmit end, in step 303, the
receive end measures power of interference included in the receive
signal. For example, the receive end measures power of a combination of
noise and interference using a pilot signal included in the receive
signal. Also, the receive end sums up power of unused tones and
recognizes the summed power as a thermal noise. After that, the receive
end removes thermal noise from the power of the combination of noise and
interference, and measures interference power.

[0058] After measuring the interference power, the receive end proceeds to
step 305 and compares the interference power measured in step 303 to a
threshold interference power so as to determine if there is interference.

[0059] If the interference power measured in step 303 is greater than the
threshold interference power, the receive end recognizes that there is
interference. Accordingly, the receive end proceeds to step 307 and
selects a pre-whitening inverse matrix (L) as a whitening control
variable. In this case, the receive end turns ON a whitening function of
a whitening MRC and receives a signal in an MMSE scheme.

[0060] On the other hand, if the interference power measured in step 303
is less than or equal to the threshold interference power, the receive
end recognizes that there is no interference. Accordingly, the receive
end proceeds to step 309 and selects a unit matrix (kI) as the whitening
control variable. In this case, the receive end turns OFF the whitening
function of the whitening MRC and receives a signal in an MRC scheme.

[0061] After that, the receive end terminates the procedure according to
the embodiment of the present invention.

[0062] In the aforementioned embodiment, a receive end selectively
provides a pre-whitening inverse matrix depending on the existence or
absence of interference.

[0063] In another embodiment, a receive end can also control an Rnn
update variable and turn ON/OFF a whitening function of a whitening MRC.
For example, the receive end converts an `Rnn` into an `LLH`
form through Cholesky Factorization as given in Equation (3). Before
carrying out Cholesky Factorization of the `Rnn`, the receive end
updates the `Rnn` as given in Equation (6).

[0065] As in Equation (6), the receive end updates `Rnn` before
generating a pre-whitening inverse matrix (L) through Cholesky
Factorization of `Rnn`. At this time, the receive end can turn
ON/OFF the whitening function of the whitening MRC depending on `k`. For
example, when there is inter-cell interference, the receive end sets `k`
down and does not vary Rnn`. As another example, when there is no
inter-cell interference, the receive end sets `k` up. In this case,
diagonal elements of `hd nn` are relatively greater than off-diagonal
elements and thus `Rnn` approaches a unit matrix. When the
`Rnn` is a unit matrix, even the pre-whitening inverse matrix (L)
becomes a unit matrix and thus, the whitening function can turn OFF.

[0066] Accordingly, the filter controllers 209-1 to 209-NR of FIG. 2
can determine an update variable for a covariance matrix (Rnn) of
noise plus interference in consideration of the influence of
interference. The filter controllers 209-1 to 209-NR calculate
pre-whitening inverse matrices (L) using the `Rnn` updated using the
update variable, and transmit the calculated pre-whitening inverse
matrices (L) to the pre-whitening filter 211.

[0067] The following description is made for a method for controlling an
Rnn update variable and turning ON/OFF a whitening function of a
whitening MRC in a receive end.

[0068] FIG. 4 is a flow diagram illustrating controlling a whitening
function depending on an interference amount in a receive end according
to another embodiment of the present invention.

[0069] Referring to FIG. 4, in step 401, the receive end identifies if a
signal is received from a transmit end.

[0070] If the signal is received from the transmit end, in step 403, the
receive end measures power of interference included in the receive
signal. For example, the receive end measures power of a combination of
noise and interference, using a pilot signal included in the receive
signal. Also, the receive end sums up power of unused tones and
recognizes the summed power as thermal noise. The receive end then
removes the thermal noise from the power of combination of noise and
interference, and measures interference power.

[0071] After measuring the interference power, the receive end proceeds to
step 405 and compares the interference power measured in step 403 with a
threshold interference power in order to determine if there is
interference.

[0072] If the interference power measured in step 403 is greater than the
threshold interference power, the receive end recognizes that there is
interference. Accordingly, the receive end proceeds to step 407 and sets
an Rnn update variable (k) to a value less than a threshold value.
Here, the threshold value includes a value for determining if a
covariance matrix (Rnn) is varied through the Rnn update
variable (k).

[0073] Then, the receive end proceeds to step 409 and calculates a
covariance matrix (Rnn) of noise plus interference.

[0074] On the other hand, if the interference power measured in step 403
is less than or equal to the threshold interference power, the receive
end recognizes that there is no interference. Accordingly, the receive
end proceeds to step 415 and sets the Rnn update variable (k) to a
value greater than the threshold value.

[0075] Then, the receive end proceeds to step 409 and calculates a
covariance matrix (Rnn) of noise plus interference.

[0076] After calculating the covariance matrix (Rnn) of noise plus
interference, the receive end proceeds to step 411 and updates the
covariance matrix (Rnn) using the Rnn update variable (k) set
in step 407 or 415. For example, the receive end updates the `Rnn`
as given in Equation (6).

[0077] After updating Rnn, the receive end proceeds to step 413 and
calculates a pre-whitening inverse matrix (L) through Cholesky
Factorization of the Rnn updated in step 411. For example, when
there is no interference and thus the Rnn update variable (k) is set
to a value greater than the threshold value, the Rnn approaches a
unit matrix because diagonal elements of the Rnn are relatively
greater than off-diagonal elements. In this case, even the pre-whitening
inverse matrix (L) becomes a unit matrix and thus, the receive end turns
OFF a whitening function of a whitening MRC and receives a signal in an
MRC scheme. As another example, when there is interference and thus the
Rnn update variable (k) is set to a value less than the threshold
value, Rnn does not vary. Accordingly, the receive end can turn ON
the whitening function of the whitening MRC and receive a signal in an
MMSE scheme.

[0078] After that, the receive end terminates the procedure according to
the embodiment of the present invention.

[0079] In the aforementioned embodiment, a receive end determines if there
is interference using interference power.

[0080] In another embodiment, a receive end can also determine if there is
interference using a Carrier to Interference plus Noise Ratio (CINR).

[0081] The following description is a method for determining a
pre-whitening control variable depending on the existence or absence of
interference that is identified using a CINR.

[0082] FIG. 5 is a flow diagram illustrating controlling a whitening
function depending on a CINR in a receive end according to an embodiment
of the present invention.

[0083] Referring to FIG. 5, in step 501, the receive end identifies if a
signal is received from a transmit end.

[0084] If the signal is received from the transmit end, in step 503, the
receive end calculates a Carrier to Interference plus Noise Ratio (CINR)
for the receive signal.

[0085] After measuring the CINR, the receive end proceeds to step 505 and
compares the CINR calculated in step 503 with a threshold CINR
(CINRTh) in order to determine if there is interference.

[0086] If the CINR calculated in step 503 is less than or equal to the
threshold CINR (CINRTh), the receive end recognizes that there is
interference. Accordingly, the receive end proceeds to step 507 and
selects a pre-whitening inverse matrix (L) as a whitening control
variable. In this case, the receive end turns ON a whitening function of
a whitening MRC and receives a signal in an MMSE scheme.

[0087] On the other hand, if the CINR calculated in step 503 is greater
than the threshold CINR (CINRTh), the receive end recognizes that
there is no interference. Accordingly, the receive end proceeds to step
509 and selects a unit matrix (kI) as the whitening control variable. In
this case, the receive end turns OFF the whitening function of the
whitening MRC and receives a signal in an MRC scheme.

[0088] After that, the receive end terminates the procedure according to
the embodiment of the present invention.

[0089] In the aforementioned embodiment, a receive end selectively
provides a pre-whitening inverse matrix depending on the existence or
absence of interference.

[0090] In another embodiment, a receive end can also control an Rnn
update variable and turn ON/OFF a whitening function of a whitening MRC.

[0091]FIG. 6 is a flow diagram illustrating controlling a whitening
function depending on a CINR in a receive end of according to another
embodiment of the present invention.

[0092] Referring to FIG. 6, in step 601, the receive end identifies if a
signal is received from a transmit end.

[0093] If the signal is received from the transmit end, in step 603, the
receive end calculates a CINR for the receive signal.

[0094] After measuring the CINR, the receive end proceeds to step 605 and
compares the CINR calculated in step 603 with a threshold CINR
(CINRTh) in order to determine if there is interference.

[0095] If the CINR calculated in step 603 is less than or equal to the
threshold CINR (CINRTh), the receive end recognizes that there is
interference. Accordingly, the receive end proceeds to step 607 and sets
an Rnn update variable (k) to a value less than a threshold value.

[0096] Then, the receive end proceeds to step 609 and calculates a
covariance matrix (Rnn) of noise plus interference.

[0097] On the other hand, if the CINR calculated in step 603 is greater
than the threshold CINR (CINRTh), the receive end recognizes that
there is no interference. Accordingly, the receive end proceeds to step
615 and sets the Rnn update variable (k) to a value greater than the
threshold value.

[0098] Then, the receive end proceeds to step 609 and calculates a
covariance matrix (Rnn) of noise plus interference.

[0099] After calculating the covariance matrix (Rnn) of noise plus
interference, the receive end proceeds to step 611 and updates the
covariance matrix (Rnn) using the Rnn update variable (k) that
is set in step 607 or step 615. For example, the receive end updates the
Rnn as given in Equation (6).

[0100] After updating the Rnn, the receive end proceeds to step 613
and calculates a pre-whitening inverse matrix (L) through Cholesky
Factorization of the Rnn updated in step 611. For example, when
there is no interference and thus the Rnn update variable (k) is set
to a value greater than the threshold value, the Rnn approaches a
unit matrix because diagonal elements of the Rnn are relatively
greater than off-diagonal elements. In this case, even the pre-whitening
inverse matrix (L) becomes a unit matrix and thus, the receive end turns
OFF a whitening function of a whitening MRC and receives a signal in an
MRC scheme. As another example, when there is interference and thus the
Rnn update variable (k) is set to a value less than the threshold
value, the Rnn does not vary. Accordingly, the receive end can turn
ON the whitening function of the whitening MRC and receive a signal in an
MMSE scheme.

[0101] After that, the receive end terminates the procedure according to
the embodiment of the present invention.

[0102] The present invention has an advantage of being capable of
improving a reception performance of a receive end by selectively using
an MMSE scheme or an MRC scheme depending on the existence or absence of
inter-cell interference in the receive end of a multiple antenna system.

[0103] While the invention has been shown and described with reference to
certain preferred embodiments thereof, it will be understood by those
skilled in the art that various changes in form and details may be made
therein without departing from the spirit and scope of the invention as
defined by the appended claims.